1. Field Of Invention
This invention relates primarily to a new and improved induction heating apparatus designed for use with metal-based cookware.
More particularly, the invention relates to a new and improved induction heating apparatus employing novel chopper inverter power supply circuits having improved operating characteristics and novel control gating circuit arrangements using new and improved infra-red heat sensing and coil arrangements for directly sensing and controlling the temperature of metal-based cookware or other objects being heated with an induction heating coil. The improved induction heating apparatus provides rapid, safe, clean and efficient heating which can be accurately controlled in a manner which minimizes the production and loss of waste heat, and accomplishes this with compact equipment of relatively low cost and not too complex design.
2. Prior Art Situation
Heretofore electrically operated home cooking appliances have employed resistance heating almost universally to convert electric into heat energy for home cooking purposes. While there are exceptions, such as are exemplified by the micro-wave heating ovens, for the most part, known electrical heating appliances use resistance heating. With such appliances the heat generated is proportional to I.sup.2 R where I is the current supplied to the resistance heating element and R is the resistance of the heating element. By switching or otherwise controlling the values of R and/or controlling I, the heat generated by a resistance heating unit can be controlled comparatively easily dependant upon the degree of control desired. However, with all resistance heating units the heat generated is controlled by controlling in some manner the electrical energy supplied to the unit. By prior calibration, the amount of heat generated by the resistance heating unit, and hence the resulting temperature of the object being heated are somewhat and only roughly related.
Consider, for example, the well known helically coiled, flat top electric stove heating units of the "Calrod" type. These units are controlled by calibrated switches on the stove which at a given setting produce a measurable quantity of I.sup.2 R generated heat that then is thermally coupled to the object being heated such as a pan. A great deal of the generated heat is wasted and contributes to thermal pollution of the environment in which the stove is located. If the stove is located in an air conditioned kitchen, not only does the waste heat contribute to inefficiency, but also the additional cooling load imposed on the air conditioner by the waste heat contributes to further inefficiency. Over a considerable operating period such as the summer months of June through August, the accumulated inefficiencies can contribute to a significant wasteage in power and increased utility bills not to mention the added discomfort in the kitchen during the cooking periods and increased loading on the utility system during periods when predictably power shortages are most likely to occur.
In addition to the inefficiencies mentioned above, presently available electric I.sup.2 R cooking units provide no reliable control over the temperature of the pan or other objects being heated. This lack of reliable control is due to the differences in the transfer of heat to pans fabricated from different metals such as aluminum, copper, iron or alloys of metal, and the difficulty of relating the efficiency of thermal coupling to the several different types of cookware and calibrated settings of the control knob for adjusting heat generation by the resistance heating units. Hence, at best the calibrated settings at the control knobs are only an educated guess at what is the actual temperature of the pan or other object being heated. To overcome the above discussed and other deficiencies inherent in electrical resistance heating apparatus, the present invention was devised.